<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>bfc</title>
<style>
  #float {
    background: red;
     overflow: hidden;
  }

  #float .float {
    float: left;
    font-size: 30px;
  }
</style>
  </style>
</head>
<body>
  <section id="float">
    <div class="float">我是浮动元素</div>
  </section>
  
</body>
</html>